In general, each femoral prosthesis includes a more or less long shank which is embedded in the femoral stump. The part which emerges therefrom is slanted with respect to the shank or stem by about 120.degree. and serves as a base for a sphere which is intended to replace the femoral head.
Thousands of operations of this kind are carried out each year, which operation gives back a normal life to patients. For that, a greaty variety, as to shape and design, of prostheses exist, but these prostheses have certain drawbacks.
At the beginning, a standard shank was used which was locked in the femoral diaphysis with cement, but cement loses its mechanical properties in the long run, and almost all the feomral prostheses of this type finish by becoming loose with the years.
The ideal is then to do without cement and to lock the prosthesis right away by any means.
Some attempts have been made by implanting adjusted prostheses covered with microscopic roughnesses, force fitted, filling the femur to a maximum and which are rehabited by the bone in the months following the operation.
This technique has in fact two drawbacks, the first being the large number of prostheses in stock required so as to have the size which is exactly adapted to the femur of the patient, and the second being the risk of bursting the upper part of the femur due to the force fitting of these prostheses.
Compromises have been found such as the self locking prosthesis of the "Muller" type which is universally known.
Its shape is especially designed, but despite everything it uses a thin layer of cement.